METHODS: Four unique case studies of CO, all of whom experienced the same level of (acute) CO poisoning (17-29%) in the same accident. Two of the individuals were brothers (aged 25 and 33 yrs at testing) with an identical genetic disorder (syndactylism) and the other 2 were brother (aged 27 at testing) and sister. Ss were tested for neuropsychological functioning, emotional-behavioral problems, and vocational difficulties 6-7 yrs post poisoning.

RESULTS: The results indicate: (1) variable neuropsychological deficits despite similar levels of CO poisoning; (2) consistent estimated decline in intelligence; (3) similar memory decline for the 2 brothers, but not for the brother and sister; and (4) consistent late-onset emotional-behavioral difficulties. The results also suggest that the neuropsychological and emotional-behavioral deficits had an impact on the individual's ability to work.

Case Reports: On June 27, 1990, following an increase in nausea, tinnitus, dizziness, and headaches which had persisted for 3 days, four subjects self-admitted to an ER and were diagnosed with acute CO poisoning. They were subsequently flown to another hospital and given HBO therapy. The CO source was a faulty gas water heater exhaust system in a new apartment shared by the victims. COHb on admission was 25.0% (Case 1), 17.2% (Case 2), 29.1% (Case 3), and 29.1% (Case 4).

Case 1: A 25-year-old never-married Caucasian male employed as a masonry laborer. He graduated from high school with a 2.5 grade point average (GPA) and earned average scores on a state-wide educational aptitude test. Prior to CO poisoning, the man had been employed for 3 years in food service as a cook and received satisfactory performance evaluations.

At testing the man complained of significant memory and sleep difficulties. He also had frequent headaches, fatigue, and anxiety, as well as decreased interest in usual activities. The Brief Symptom Inventory (BSI) revealed significant adjustment problems, including depression, anxiety, and cognitive difficulties. Obsessive-compulsive tendencies were noted, as well as significant difficulties in relating to and interacting with others. These symptoms began approximately 5-6 years post-injury.

From the time of the accident until neuropsychological testing, this man had held seven jobs. He had complained of being unable to remember instructions, being slow and forgetful, and having difficulty with attention and concentration. At the time of testing, this man complained of difficulty remembering and comprehending complex verbal instyructions on his current job, which contributed to decreased work efficiency.

Neuropsychological testing revealed this man to be of low average intelligence, which was believed to represent a decline in functioning as compared with the reading subtest score of the Wide Range Achievement Test-III (WRAT-3). Other depressed areas of functioning were memory skills, abstract reasoning, and complex problem solving.

Case 2: At the time of testing this patient was a 33-year-old married Caucasian male employed as an injection molder. He was the brother to the man in Case 1. He had graduated from high school with a 2.5 GPA and had earned above average scores on a state-wide aptitude test. Prior to the CO poisoning, this man had been successfully employed in food service, but quit soon after due to fraustration related to slower job performance.

At testing he complained of significant residual effects including frequent headaches, short-term memory problems, and decreased attention and concentration. He said that he had difficulty waking in the morning, was often irritable, and had a lower frustration tolerance. Although the memory and learning problems began shortly after the injury, feelings of depression and anxiety increased ovber the previous two years. Emotional-behavioral testing revealed abnormal elevations on all indices; the highest being on measures of obsessive-compulsiveness, and cognitive difficulties. He had significant difficulties with interpersonal relations, depression, anxiety, and anger.

The man had a stable work history and satisfactory job performance prior to the poisoning. Since then he had held six jobs, primarily in food service, but lost those jobs due to slow, inefficient performance. On the job, he had significant problems with memory and cognitive tracking, typically having difficulty with sustained concentration. He says it takes him longer to learn new jobs and he is irritable and short-tempered.

Neuropsychological testing revealed this man to be of average intelligence, which represented a likely decline, based on his WRAT-3 reading score, subsequent to CO exposure. Significant problems were noted in immediate verbal memory and delayed memory, both of which were within the borderline mentally handicapped range.

Case 3: This was a 27-year-old married, unemployed Caucasian man. He had been employed sporadically for the past 4 years, moving and blocking mobile homes. He had graduated from high school and reported being an average student - no prior test scores were available.

This man complained of frequent headaches, which occurred frequently, typically 3-4 days during the week, and are alleviated only with sleep. He also reported decreased short-term memory and difficulty learning new information, both of which were reported to be worsening. Over the past 2 years, this man reported becoming increasingly irritable and easily angered and having a decreased tolerance for frustration. Like Cases 1 and 2, emotional-behavioral questionnaires indicated significant complaints of cognitive difficulties, anxiety, anger, and obsessive-compulsive tendencies.

The man reported that he did not lose any specific job-related skills post-injury, although he did have increased difficulties with his memory. He also complained of needing frequent verbal prompts, repeated directions, and additional/extended learning opportunities to learn new tasks, all of which represented a change from pre-injury vocational aptitude.

Neurpsychological testing indicated that this man had low average intelligence, which represented a likely decline from the pre-morbid state. His immediate visual memory was impaired, although this finding was not consistently found across all measures of memory functioning.

Case 4: This was a never-married Caucasian woman who had last worked as a cook 3 weeks prior to testing. She was the sister to the man in Case 3. She had been held back in eight-grade in school and had quit school during her 10th year. Despite variable grades throughout school, review of her academic records revealed her to have obtained average cognitive and achievement test scores on state-wide educational tests.

She reported having frequent headaches, fatigue, and emotional lability. Results of the BSI showed significant adjustment problems - these were in obsessive-complusive behaviors, hostility, and excessive fears. There were also significant problems with depression and interpersonal relations.

Since the CO poisoning, this woman had held six jobs as a cook, with the longest period of sustained employment being 18 months. She explained that her vocational deficits associated with the poisoning included forgetfulness, short-term memory problems, and difficulties retrieving previously-learned information. She also described problems with expressive language, inattentiveness, and general mental efficiency. It now takes her longer to solve routine problems.

Neuropsychological testing revealed low average intelligence, which represented a slight decline in functioning. Compared to her current intelligence, a borderline range deficit was noted in measured attention skills.

To Especially Note:

Clear cut residual physical, cognitive, and/or emotional/personality changes were evident years after the CO poisoning, regardless of the fact that the victims received HBO within 12 hours of the CO poisoning.

There was no clear relationship between COHb level at admission and residual neuropsychological deficits. This has been noted in many other studies.

All 4 cases involved declines in estimated intelligence. Three victims had educational testing prior to the CO poisoning. This is the more serious outcome as compared to simply deficits in various areas of cognition without a fall in overall intelligence.

There were similar declines in memory functioning for the two brothers, but not for the brother/sister. It is common to see a variety of effects in people exposed to CO under "identical" circumstances (presumed CO concentration x duration of exposure). These victims also were all young.